Tiny patch makes aircraft engine inspection easier

Inspecting aircraft engines for tiny cracks could soon be done on the runway thanks to a new 1cm2 testing patch.

Researchers from Nottingham University and Rolls-Royce are developing the patches as a way of creating and detecting ultrasonic waves that can be used to identify internal faults in components without the need to take the engine apart.

The team, led by Prof Matt Clark, hope this could help aircraft technicians spot potential problems earlier because they won’t have to wait for a routine engine overhaul to inspect for cracks – or spend as long carrying out this maintenance.

‘Usually the engine has to be disassembled and parts taken out for inspection, which consumes a lot of time and the plane is not operational during this time,’ Victoria Ageeva, a PhD student working on the project, told The Engineer. ‘[We hope] we can enable such inspection on the runway through existing ports in the engine.’

The patches, known as cheap optical transducers (CHOTs), are designed to create a wireless alternative to the larger piezoelectric transducer systems currently used for inspection, which must be physically connected to components.

Instead, the CHOTs should allow technicians to place a flexible fibrescope through existing openings in an engine in order to generate and detect the ultrasonic waves that can reveal internal cracks.

Each CHOT system comprises two patches: one with a particular microstructure that generates the ultrasound and another with a reflective surface that enables detection of the waves.

When a laser is shone on the structured patch, it absorbs the radiation, heats up and expands, pushing against the component beneath in a way that is designed to create ultrasonic waves in a particular direction and frequency.

A second laser is then shone on the adjacent patch, which is coated in a reflective material such as silver. A detection system picks up the reflected light waves and measures how the diffraction (bending) of the light changes as the second patch is hit by the ultrasound from the first.

This is turned into a representation of an ultrasound signal that can easily be read by a technician. Any unusual echoes in the signal indicate the presence of a fault or crack in the component.

The system is limited to detecting cracks at the point where the patches are placed, but using multiple CHOTs – which can either be built into the component or retrofitted – would allow a technician to run the fibrescope along across them to take a wider analysis of the structure.

‘Rolls-Royce says it is interested in monitoring a particular bit which they know has a lot of stress,’ said Ageeva.

The technology could also be used in other applications that require remote inspection such as in nuclear power stations, and has already been explored as a way to create injectable sensors that can be used to image cells in the body.